# 180 degree forward/reverse on/off motor

#### summersab

Joined Apr 8, 2010
146
I know this is more mechanical than electrical in nature, but I'm thinking that this may be closer to a robotics question, so perhaps someone on here has an answer. Here's basically what I have. I've got a key switch lock, and I want to push a locking pin into place using a small motor and a cam when I turn the switch on and off (i.e. voltage applied, voltage removed). The cam and pin would look something like this:

However, unlike what is being shown in this picture, I don't want to have a full rotation. I want the motor to spin 180 degrees to push the pin forward and lock and then reverse 180 degrees to release the pin.

If possible, I don't want to have to have a bunch of controller boards that need programming - perhaps just a pulse for forward and a pulse for backward. I know the question of load is going to come up, so I'll estimate that it takes about 5 lb of force to push the pin into place. What type of motor would do this?

#### TheButtonThief

Joined Feb 26, 2011
237
What you're hoping to do will require some degree of control, especially if you're using a signal (or "pulse" as you put it) to execute a function. Do you know what motor you're using? Only a stepper motor has the ability to turn it's armature in precise increments but because the motor doesn't know what position it's armature is in or what "180 degrees" is, you have to tell it and the only way to do that is to use a controller. The controller will need position sensors so that it knows the relative set points such as "locked" and "un-locked" and so that it knows in what direction it must turn the motor and when it must stop turning it.

If this design criteria is acceptable, then I'd be happy to help you work out a solution, it's actually quite simple.

Jay

Joined Jul 18, 2013
22,005
The force (torque) needed would be 5lb x the distance from the centre of rotation to the cam pin, lb-in.
If I understand correctly then you would need another cam operator at 180° to reverse the pin?
What is the arrow indicating?
If using a motor there is way to do it with relay logic and use a small sensor at each end of the pin move extent.
This could be miniature prox sensors etc.
Max.

#### summersab

Joined Apr 8, 2010
146
I'll be really specific. You know those military-style canvas webbed belts?

I'm not using it as a belt, exactly, but I'm trying to mount something to the underside that will force the pin forward and then release it. I intend to cut a slit in the underside of the buckle to let whatever mechanism come up through the bottom to actuate the pin. Note that the pin has burrs on it, so I can't have a lobed gear rub on it - it will wear out.

#### summersab

Joined Apr 8, 2010
146
Perhaps I should have started with a mechanical forum. I just hate signing up for new forums just to ask a single question and never return...

Joined Jul 18, 2013
22,005
There are a few of us here that are versed in Mechatronics. And do it for a living.
It is just that it is imperative to have the details!

Max.

#### AnalogKid

Joined Aug 1, 2013
8,806
One way to reduce the control goop needed is to add limit switches to the mechanical assembly:

Turn the key switch to lock.
The motor runs in the extend direction until something hits the extend limit switch.
Motor stops and sits.
Turn the key switch to unlock.
Motor runs in the retract direction until something hits the retract limit switch.
Motor stops and sits.
etc.

Besides the two limit switches, all of the control can be done with one relay and two diodes.

ak